Documentation/sysfs-rules.txt: convert it to ReST markup

- Fix document title;
- use quote blocks where needed;
- use monotonic fonts for config options and file names;
- adjust whitespaces and blank lines;
- add it to the user's book.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/sysfs-rules.txt

 Rules on how to access information in the Linux kernel sysfs
+============================================================
 
 The kernel-exported sysfs exports internal kernel implementation details
 and depends on internal kernel structures and layout. It is agreed upon
@@ -27,10 +28,10 @@ versions of the sysfs interface.
     to sysfs has failed; it causes more problems than it solves. It
     violates many of the rules in this document.
 
-- sysfs is always at /sys
-  Parsing /proc/mounts is a waste of time. Other mount points are a
+- sysfs is always at ``/sys``
+    Parsing ``/proc/mounts`` is a waste of time. Other mount points are a
     system configuration bug you should not try to solve. For test cases,
-  possibly support a SYSFS_PATH environment variable to overwrite the
+    possibly support a ``SYSFS_PATH`` environment variable to overwrite the
     application's behavior, but never try to search for sysfs. Never try
     to mount it, if you are not an early boot script.
 
@@ -42,12 +43,14 @@ versions of the sysfs interface.
     applications that look for devices in sysfs.
 
     The properties of a device are:
-    o devpath (/devices/pci0000:00/0000:00:1d.1/usb2/2-2/2-2:1.0)
+
+    - devpath (``/devices/pci0000:00/0000:00:1d.1/usb2/2-2/2-2:1.0``)
+
       - identical to the DEVPATH value in the event sent from the kernel
         at device creation and removal
       - the unique key to the device at that point in time
       - the kernel's path to the device directory without the leading
-        /sys, and always starting with a slash
+        ``/sys``, and always starting with a slash
       - all elements of a devpath must be real directories. Symlinks
         pointing to /sys/devices must always be resolved to their real
         target and the target path must be used to access the device.
@@ -56,17 +59,20 @@ versions of the sysfs interface.
       - using or exposing symlink values as elements in a devpath string
         is a bug in the application
 
-    o kernel name (sda, tty, 0000:00:1f.2, ...)
+    - kernel name (``sda``, ``tty``, ``0000:00:1f.2``, ...)
+
       - a directory name, identical to the last element of the devpath
-      - applications need to handle spaces and characters like '!' in
+      - applications need to handle spaces and characters like ``!`` in
         the name
 
-    o subsystem (block, tty, pci, ...)
+    - subsystem (``block``, ``tty``, ``pci``, ...)
+
       - simple string, never a path or a link
       - retrieved by reading the "subsystem"-link and using only the
         last element of the target path
 
-    o driver (tg3, ata_piix, uhci_hcd)
+    - driver (``tg3``, ``ata_piix``, ``uhci_hcd``)
+
       - a simple string, which may contain spaces, never a path or a
         link
       - it is retrieved by reading the "driver"-link and using only the
@@ -75,7 +81,8 @@ versions of the sysfs interface.
         driver; copying the driver value in a child device context is a
         bug in the application
 
-    o attributes
+    - attributes
+
       - the files in the device directory or files below subdirectories
         of the same device directory
       - accessing attributes reached by a symlink pointing to another device,
@@ -86,7 +93,7 @@ versions of the sysfs interface.
 
 - Properties of parent devices never belong into a child device.
     Always look at the parent devices themselves for determining device
-  context properties. If the device 'eth0' or 'sda' does not have a
+    context properties. If the device ``eth0`` or ``sda`` does not have a
     "driver"-link, then this device does not have a driver. Its value is empty.
     Never copy any property of the parent-device into a child-device. Parent
     device properties may change dynamically without any notice to the
@@ -94,37 +101,37 @@ versions of the sysfs interface.
 
 - Hierarchy in a single device tree
     There is only one valid place in sysfs where hierarchy can be examined
-  and this is below: /sys/devices.
+    and this is below: ``/sys/devices.``
     It is planned that all device directories will end up in the tree
     below this directory.
 
 - Classification by subsystem
     There are currently three places for classification of devices:
-  /sys/block, /sys/class and /sys/bus. It is planned that these will
+    ``/sys/block,`` ``/sys/class`` and ``/sys/bus.`` It is planned that these will
     not contain any device directories themselves, but only flat lists of
-  symlinks pointing to the unified /sys/devices tree.
+    symlinks pointing to the unified ``/sys/devices`` tree.
     All three places have completely different rules on how to access
     device information. It is planned to merge all three
-  classification directories into one place at /sys/subsystem,
+    classification directories into one place at ``/sys/subsystem``,
     following the layout of the bus directories. All buses and
     classes, including the converted block subsystem, will show up
     there.
     The devices belonging to a subsystem will create a symlink in the
-  "devices" directory at /sys/subsystem/<name>/devices.
+    "devices" directory at ``/sys/subsystem/<name>/devices``,
 
-  If /sys/subsystem exists, /sys/bus, /sys/class and /sys/block can be
-  ignored. If it does not exist, you always have to scan all three
+    If ``/sys/subsystem`` exists, ``/sys/bus``, ``/sys/class`` and ``/sys/block``
+    can be ignored. If it does not exist, you always have to scan all three
     places, as the kernel is free to move a subsystem from one place to
     the other, as long as the devices are still reachable by the same
     subsystem name.
 
-  Assuming /sys/class/<subsystem> and /sys/bus/<subsystem>, or
-  /sys/block and /sys/class/block are not interchangeable is a bug in
+    Assuming ``/sys/class/<subsystem>`` and ``/sys/bus/<subsystem>``, or
+    ``/sys/block`` and ``/sys/class/block`` are not interchangeable is a bug in
     the application.
 
 - Block
-  The converted block subsystem at /sys/class/block or
-  /sys/subsystem/block will contain the links for disks and partitions
+    The converted block subsystem at ``/sys/class/block`` or
+    ``/sys/subsystem/block`` will contain the links for disks and partitions
     at the same level, never in a hierarchy. Assuming the block subsystem to
     contain only disks and not partition devices in the same flat list is
     a bug in the application.
@@ -132,26 +139,26 @@ versions of the sysfs interface.
 - "device"-link and <subsystem>:<kernel name>-links
     Never depend on the "device"-link. The "device"-link is a workaround
     for the old layout, where class devices are not created in
-  /sys/devices/ like the bus devices. If the link-resolving of a
-  device directory does not end in /sys/devices/, you can use the
-  "device"-link to find the parent devices in /sys/devices/. That is the
+    ``/sys/devices/`` like the bus devices. If the link-resolving of a
+    device directory does not end in ``/sys/devices/``, you can use the
+    "device"-link to find the parent devices in ``/sys/devices/``, That is the
     single valid use of the "device"-link; it must never appear in any
     path as an element. Assuming the existence of the "device"-link for
-  a device in /sys/devices/ is a bug in the application.
-  Accessing /sys/class/net/eth0/device is a bug in the application.
+    a device in ``/sys/devices/`` is a bug in the application.
+    Accessing ``/sys/class/net/eth0/device`` is a bug in the application.
 
-  Never depend on the class-specific links back to the /sys/class
+    Never depend on the class-specific links back to the ``/sys/class``
     directory.  These links are also a workaround for the design mistake
-  that class devices are not created in /sys/devices. If a device
+    that class devices are not created in ``/sys/devices.`` If a device
     directory does not contain directories for child devices, these links
-  may be used to find the child devices in /sys/class. That is the single
+    may be used to find the child devices in ``/sys/class.`` That is the single
     valid use of these links; they must never appear in any path as an
     element. Assuming the existence of these links for devices which are
-  real child device directories in the /sys/devices tree is a bug in
+    real child device directories in the ``/sys/devices`` tree is a bug in
     the application.
 
     It is planned to remove all these links when all class device
-  directories live in /sys/devices.
+    directories live in ``/sys/devices.``
 
 - Position of devices along device chain can change.
     Never depend on a specific parent device position in the devpath,
@@ -159,7 +166,7 @@ versions of the sysfs interface.
     the chain. You must always request the parent device you are looking for
     by its subsystem value. You need to walk up the chain until you find
     the device that matches the expected subsystem. Depending on a specific
-  position of a parent device or exposing relative paths using "../" to
+    position of a parent device or exposing relative paths using ``../`` to
     access the chain of parents is a bug in the application.
 
 - When reading and writing sysfs device attribute files, avoid dependency
@@ -170,10 +177,11 @@ versions of the sysfs interface.
     propagate errors wherever possible. Common errors include, but are not
     limited to:
 
-  -EIO: The read or store operation is not supported, typically returned by
-        the sysfs system itself if the read or store pointer is NULL.
+	``-EIO``: The read or store operation is not supported, typically
+	returned by the sysfs system itself if the read or store pointer
+	is ``NULL``.
 
-  -ENXIO: The read or store operation failed
+	``-ENXIO``: The read or store operation failed
 
     Error codes will not be changed without good reason, and should a change
     to error codes result in user-space breakage, it will be fixed, or the